A mobile telecommunications subscriber is normally associated with a home network which normally is the mobile telecommunications network of the service provider with which the subscriber has entered into a mobile telecommunications agreement. In the home network, a phone number is assigned to the subscriber, and additional subscriber data is registered, which is associated with subscription data that is checked, particularly when the subscriber signs in to a mobile telecommunications network. The subscription data comprises a subscriber identifier and additional authentication parameters, and this data is normally stored in a subscriber identifier configured as a chip card that is inserted into the mobile telecommunications device of the subscriber.
Using his/her subscription data, a subscriber of a home network can also sign in to external networks, provided that they allow access by subscribers of this home network. This capability is also referred to as roaming and it makes it possible to use mobile telecommunications services when the subscriber is currently in a geographical region in which the home network is not available. In order to authenticate the subscriber, external networks normally make use of the subscriber data that is registered in the home network of the subscriber, and the subscriber can be reached in an external network at the phone number that is valid in the home network.
However, a drawback of roaming is that normally higher fees are charged for using mobile telecommunications services in external networks. Moreover, it is often the case that certain mobile telecommunications services such as, for example, data services, can only be used to a limited extent or can even be blocked entirely.
In order to access mobile telecommunications services in regions that are not covered by the home network and in order to avoid the drawbacks of roaming, a mobile telecommunications subscriber can enter into additional mobile telecommunications agreements with mobile telecommunications service providers whose mobile telecommunications networks provide services in the regions in question. In this manner, the mobile telecommunications subscriber can access several home networks that can cover several geographical regions. However, for each of the different home networks, he/she receives a subscriber identification card that especially contains the subscription data for the home network in question, and he/she has to use the matching subscriber identification card in each of his/her home networks in order to avoid roaming.
In order to use the subscriber identification card of the available home network in each case, the mobile telecommunications user can switch the subscriber identification card inside his/her mobile telecommunications devices when he/she changes to another home network. However, this is awkward and also means that they cannot be reached at the phone number that is associated with him/her in another home network. As an alternative, the subscriber can use several mobile telecommunications devices that each contain one of the subscriber identification cards. This, however, also involves considerable effort.
Another possibility for using subscription data for different home networks is the mobile telephone described in EP 1 231 800 A1, which can hold and use multiple subscriber identification cards. However, this option means that the user is limited to using a special device that has holders for two subscriber identification cards.